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Discovered: October 09, 2003
Updated: February 13, 2007 12:08:53 PM
Also Known As: BackDoor.BAM [McAfee], BKDR_SINIT.A [Trend], Win32.Sinit [Computer Associat, Backdoor.Sinit [Kaspersky], Troj/BDSinit [Sophos]
Type: Trojan Horse
Systems Affected: Windows

Backdoor.Sinit is a Backdoor Trojan horse that gives an attacker unauthorized access to a compromised computer, by opening a random UDP port.

Backdoor.Sinit is written in the Microsoft Visual C++ programming language and is compressed with UPX.

Antivirus Protection Dates

  • Initial Rapid Release version October 10, 2003
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version October 10, 2003
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date October 15, 2003

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Ying Lin

Discovered: October 09, 2003
Updated: February 13, 2007 12:08:53 PM
Also Known As: BackDoor.BAM [McAfee], BKDR_SINIT.A [Trend], Win32.Sinit [Computer Associat, Backdoor.Sinit [Kaspersky], Troj/BDSinit [Sophos]
Type: Trojan Horse
Systems Affected: Windows

When Backdoor.Sinit is executed, it does the following:

  1. Copies itself as %System%\Svcinit.exe, which runs in the background and deletes the original file.

    Note: %System% is a variable. The Trojan locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  2. In Windows 95, Windows 98, and Windows Millennium Edition (Me):

    adds the value:

    "SVC Service" = "%System%\svcinit.exe"

    to the registry key:


    so that the Trojan runs when you start Windows.

  3. In Windows NT, 2000, and XP:

    modifies the value:

    "Userinit" = "%System%\userinit.exe"

    in the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\

    so that the Trojan runs when you log on.

  4. Creates the following registry key:


  5. Opens a random UDP port that may allow a hacker to perform any of the following actions:
    • Obtain computer and network information
    • Perform annoying actions
    • Intercept confidential information by hooking keystrokes
    • Download and execute files
    • Manage the installation of the Trojan
    • Alter system parameters


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

Writeup By: Ying Lin

Discovered: October 09, 2003
Updated: February 13, 2007 12:08:53 PM
Also Known As: BackDoor.BAM [McAfee], BKDR_SINIT.A [Trend], Win32.Sinit [Computer Associat, Backdoor.Sinit [Kaspersky], Troj/BDSinit [Sophos]
Type: Trojan Horse
Systems Affected: Windows

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Update the virus definitions.
  2. Do one of the following:
    • Windows 95/98/Me: Restart the computer in Safe mode.
    • Windows NT/2000/XP: End the Trojan process.
  3. Run a full system scan and delete all the files detected as Backdoor.Sinit.
  4. Reverse the changes that were made to the registry
For specific details on each of these steps, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.
2. Restarting the computer in Safe mode or ending the Trojan process
    Windows 95/98/Me
    Restart the computer in Safe mode. All the Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions, read the document How to start the computer in Safe Mode.

    Windows NT/2000/XP
    To end the Trojan process:
    1. Press Ctrl+Alt+Delete once.
    2. Click Task Manager.
    3. Click the Processes tab.
    4. Double-click the Image Name column header to alphabetically sort the processes.
    5. Scroll through the list and look for "Svcinit.exe."
    6. If you find the file, click it, and then click End Process.
    7. Exit the Task Manager.

3. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with Backdoor.Sinit, click Delete. If you are running Windows 2000 or XP, and the scan cannot delete the detected file, restart the computer in Safe mode and run the scan again.

4. Reversing the changes made to the registry

WARNING: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.

  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit

    Then click OK. (The Registry Editor opens.)

  3. Do one of the following:
    • Windows 95/98/Me
      1. Navigate to the key:


      2. In the right pane, delete the value:

        "SVC Service"="%System%\svcinit.exe"

    • Windows NT/2000/XP:
      1. Navigate to the key:

        HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
      2. In the right pane, double-click the value:

      3. In the Value data box, delete all text to the right of the comma. Do not delete the comma itself.

        For example, on a default installation, change:




  4. Navigate to and delete the registry key:


  5. Exit the Registry Editor.

Writeup By: Ying Lin